Sulaiman, Muhammad Syahir, and WAN MOHD WARDI WAN ABDUL RAHMAN. “Study of Potential of Polyethylene Foam As Sound Insulation for HVAC Rectangular Duct”. Progress in Engineering Application and Technology, vol. 2, no. 1, June 2021, pp. 779-86, https://penerbit.uthm.edu.my/periodicals/index.php/peat/article/view/716.